Manufacturing of integrated circuits has been enabled by high-performance spin-on organic polymeric resists. In addition to sensitivity and resolution requirements, resists must maintain critical linewidth control throughout the patterning process, including both imaging and subsequent transfer via processes such as plasma etch. For example, line-edge roughness on the order of 5-10 nm is a concern at 250 nm, but can render a lithographic process unworkable when critical dimensions fall to below 100 nm.
For many photolithographic techniques, a sensitivity-throughput relationship exists. In particular, increasing the sensitivity of a resist to lithographic radiation can improve process throughput by decreasing the amount of lithographic radiation needed to achieve a particular resist disposition. Thus, techniques that sensitize resists utilized at conventional electromagnetic radiation wavelengths (e.g., about 193 nm or about 157 nm) for lithography can help improve current lithographic processes.
In addition, advances in resist sensitization could enable emerging lithographic techniques for producing very small feature devices. In recent years, advanced devices have had their half-pitch at 90 nm using 193-nm dry exposures, and it is widely expected to extend to 45-nm half-pitch by incorporating liquid immersion. Indeed, according to the international roadmap for semiconductors (ITRS), this trend will continue unabated for at least one more decade with expected resolution decreasing to 45 nm in 2010, and 32 nm in 2013. Accordingly, a need exists to develop future imaging technologies such as extreme ultraviolet (EUV) lithography or maskless electron beam.
EUV lithography employs extremely small wavelength photons (13.4 nm) in imaging. It is thought that EUV will be employed to 32-nm half-pitch and possibility down to 25-nm half-pitch when finally developed. One difficulty with EUV is the lack of a high power photon source, which will limit the manufacturing throughput without the introduction of very high sensitivity resists. To get high-throughput EUV systems, the laser source must be improved to generate more of the extreme ultraviolet radiation, or light. Today's best YAG lasers generate only about 10 Watts of radiation. The power level must be boosted to 100 Watts or more for high-throughput commercial production. Even at this power level, resist sensitivity must improve significantly.
Maskless electron beam lithography has intrinsically high resolution. Its current limitation, however, is relatively low throughput. Until recently, this limitation far outweighed cost considerations of optical projection systems and photomasks. However, the balance is beginning to tilt in the other direction, both because optical lithography is becoming increasingly expensive and because novel concepts of electron-beam systems may significantly boost their throughput. Enhanced throughputs may be sufficient to enable prototyping at reduced cost and turnaround time, and even enable cost-effective production of low-volume (<1000 wafer) device runs. Nonetheless, for maskless electron-beam lithography to be successfully utilized in integrated circuit fabrication, resist sensitivity will have to be significantly increased.
Accordingly, a need exists for resist formulations and components thereof that will increase the resist sensitivity to imaging lithographic radiation. As well, it is advantageous to achieve such increases in sensitivity without substantial increases in linewidth roughness.